The electrocardiogram has several advantages in detecting cardiac arrhythmia-it is readily available, noninvasive and cost-efficient. Recent genome-wide association studies have identified single-nucleotide polymorphisms that are associated with electrocardiogram measures. We performed a genome-wide association study using Korea Association Resource data for the discovery phase (Phase 1, n = 6805) and two consecutive replication studies in Japanese populations (Phase 2, n = 2285; Phase 3, n = 5010) for QRS duration and PR interval. Three novel loci were identified: rs2483280 (PRDM16 locus) and rs335206 (PRDM6 locus) were associated with QRS duration, and rs17026156 (SLC8A1 locus) correlated with PR interval. PRDM16 was recently identified as a causative gene of left ventricular non-compaction and dilated cardiomyopathy in 1p36 deletion syndrome, which is characterized by heart failure, arrhythmia and sudden cardiac death. Thus, our finding that a PRDM16 SNP is linked to QRS duration strongly implicates PRDM16 in cardiac function. In addition, C allele of rs17026156 increases PR interval (beta ± SE, 2.39 ± 0.40 ms) and exists far more frequently in East Asians (0.46) than in Europeans and Africans (0.05 and 0.08, respectively).